Richard Linklater's new movie Boyhood is, as its title suggests, a movie about a boy. But the movie's emotional center of gravity lies not in his story, but in that of his mother's.

Olivia, played by Patricia Arquette, is a single-mother who struggles to raise her two kids, the eponymous Mason and his older sister Samantha. She loves her children, but the film does not define her only by her love. No, Olivia's story is clearly presented as one of gains and losses, ecstasy and despair. Her affection for her children and the constant, often thankless, sacrifices she must make for them exist side-by-side, neither having more of a hold on how she viewed her life or on how we, the audience, are encouraged to view her.

This portrayal of motherhood in neither sentimental or unsentimental terms is unusual, and the crowning achievement of what is an altogether stellar film.

(It is impossible to carry on without spoilers. So if you haven't seen the film yet, I suggest you bookmark this and come back afterwards.)

If this observational film has a climax, I'd argue that it arrives at the very end when Mason leaves for college and Olivia, who raised her kids on her own, says: "I knew this day was coming. I just didn't realize you'd be so fucking happy to be leaving. I just thought there would be more."

More. It's a reasonable request coming from a woman who raised her kids essentially on her own, with infrequent guest appearances from their father, played by Ethan Hawke, the freewheeling aspiring musician whose arrested development and vintage sports car get in the way of him having a more regular role in their lives. In the course of the movie Olivia is forced to move a number of times. We directly experience the visceral mourning of the children who are forced to leave, again and again, the place they call home. In an early scene we see a young Mason applying white paint over a growth chart on a door pane, his first warning against erecting totems of any sort and expecting them to last. Olivia's grief, however, is kept on the back-burner, though as things carry on it becomes impossible to ignore.

Why does she move? Desperation and bad choices — mostly fueled by desperation. Because she needs a better job and requires an education and her mother's help to get one. Because her alcoholic husband beats her. Because she purchases a home she can't really afford with another husband who ends up being unreliable. Because she has her own dream too of becoming a psychology professor, and saw to achieving it. All the while her children behave as children do, thinking mostly about themselves and what she isn't able to give them. Their logic, shared by most of us until we reach true adulthood, is that mothers are there to give — and give and give — and when the giving stops we have the right to protest. Rare is the child who stops to think about whether his or her mother has given all she can. I suspect much of this parent-child dynamic is built into our DNA. What isn't is the idea that mothers have to do all this giving on their own.

Compare Olivia's final words, "I just thought there would be more," to the pot-fueled revelation delivered by Mason at the film's end: "Yeah, I know, it's constant, the moments, it's just — it's like it's always right now, you know?" This line cuts right to what separates the son from his mother: He sees the "right now," a piece of fruit ripe for the taking; his mom knows what happens when that fruit goes spoiled because there was no time to eat it.